This invention relates to positioning a patient using a fixture that is customized for that patient.
In many medical procedures, it is desirable or necessary for a patient to be fixed in position (location and orientation) relative to a medical apparatus during the procedure. For example, a patient""s head may be restrained during a scanning procedure in a device such as a CT or MRI scanner. After such a scanning procedure, a coordinate system of the scanned image is often mapped, or xe2x80x9cregistered,xe2x80x9d to a physical coordinate system to provide a way of physically locating features that are visible in the scanned image. Fiducial markers, which can be anatomical structures or devices attached to the body, serve as reference points for the physical coordinate system. If a subsequent scan is performed, for example using a different scanning technique, the multiple scans can be registered to a common physical coordinate system in order to view the same features in the different scanned images.
In some medical procedures, it is also desirable or necessary to repeatedly position a patient in a particular location and orientation relative to the medical apparatus on a number of separate occasions. For example, a patient may return on multiple days for radiation therapy (radiotherapy) in which a beam of radiation is directed toward a particular feature in the body (a xe2x80x9ctargetxe2x80x9d) such as a cancerous tumor. One approach to targeting the same feature at each session is, at each session, to first restrain the patient relative to the apparatus and then to determine the location of the target relative to the apparatus, for example, using the locations of fiducial markers on patient. In one approach, a xe2x80x9cbite platexe2x80x9d with trackable markers is used to determine the position of the patient relative to a medical apparatus using a remote sensing system. The medical apparatus is adjusted according to the sensed position of the patient. Another approach to targeting the same feature at each session is to restrain the patient in precisely the same position relative to the apparatus at each session. In one such approach, a complex, cumbersome, and often painful positioning device, such as a stereotactic head frame, is fixed to a patient prior to scanning. The device is left in place after scanning to later position or register the patient in the medical apparatus. In another approach to repeatable positioning, a molded synthetic cast of a patient""s head is made, and split in half to allow removal and subsequent re-attachment to the head. A stereotactic frame is attached to the mold, thereby allowing repeatable positioning of the stereotactic frame. Features in the body are then targeted relative to the stereotactic frame.
In one aspect, in general, the invention is a method for positioning a body in relation to a medical apparatus using a customized positioning fixture. Mounting data that characterizes positions of a number of mounting locations on the body is first determined. Using this mounting data, a digital model of the positioning fixture is computed. The digital model characterizes a shape of the positioning fixture such that the shape includes a first set of mounting structures that mate with the mounting locations on the body, and a second set of mounting structures for attaching the positioning fixture to the medical apparatus. The positioning fixture is then fabricated according to the digital model. The body is fixed to the medical apparatus in a predetermined position of the body relative to the medical apparatus. This involves mating the first set of mounting structures with the mounting locations on the body, and attaching the positioning fixture to the medical apparatus using the second set of mounting structures.
The invention can include one or more of the following features.
Fabricating the positioning fixture includes forming a unitary structure using a computer-controlled process. The unitary structure is formed using a rapid prototyping and tooling (RPT) technique.
The method includes, after fixing the body to the medical apparatus in the predetermined position, releasing the body from the positioning fixture. Then, the steps of fixing the body to and then releasing the body from the medical apparatus are repeated. At each repetition, the body is fixed in the same predetermined position relative to the medical apparatus.
The method includes forming a three-dimensional scanned image of the body. In order to determine the mounting data, the mounting locations are identified in the scanned image.
The method includes attaching a set of mounting devices to the body prior to forming the scanned image. These mounting devices form the mounting locations on the body to which the position fixture will be fixed. The mounting devices can include bone anchors, which can be subcutaneous bone anchors.
Identifying the mounting locations in the scanned image includes identifying points on an anatomical structure of the body to which the positioning fixture will be fixed.
The shape of the positioning fixture forms a number of separate segments that together form a clamp, or other structure which mates with the anatomical structure when the positioning fixture is fixed to the body.
The medical apparatus is a scanning device. For instance, the scanning device is a CT or an MRI scanner.
The method includes determining a location of a target within the body. Using the determined location of the target, the predetermined position of the body is determined in order to position the target at a predetermined position relative to medical apparatus when the body is fixed to the apparatus using the positioning fixture.
The medical apparatus includes a radiation therapy device.
The method includes determining a second position of the body relative to a second medical apparatus. The mounting data and the determined second position are used in computing a second digital model of a second positioning fixture. The second positioning fixture is fabricated according to the second digital model. The body is then fixed to the second medical apparatus in that second position. This involves mating the second positioning fixture with the mounting locations on the body and attaching the second positioning fixture to the second medical apparatus.
The invention includes one or more of the following advantages.
By providing a way of positioning the patient in a predetermined location and orientation relative to a medical apparatus, the actual location of the patient does not need to be determined once the patient is fixed in the medical apparatus. This has a first advantage of reducing the amount of time the patient is fixed to the apparatus. A second advantage is that the patient may be more accurately positioned than can be determined after the patient is fixed by a registration procedure.
By fabricating multiple fixtures based on a single scan of the patient, each adapted to a different medical apparatus such as to different scanning devices, the relative position of the patient in the different devices can be predetermined. For instance, if two scanning devices produce planar xe2x80x9cslicesxe2x80x9d of images, then the relative position in the two scanners can be predetermined such that the slices from the two scanning devices are parallel.
By fabricating the customized fixture from a scanned image of the patient, rather than molding the fixture to the contours of the patient""s body, the patient does not suffer the inconvenience and discomfort that may be associated with that molding process.
By not requiring that the customized fixture is attached during the initial scanning, a registration process is avoided by forming the customized fixture to not only mate with the patient but to also position a device, such as a stereotactic frame, in a predetermined position relative to the patient.
Other features and advantages of the invention are apparent from the following description, and from the claims.